Without any exception, present day fail-safe or auto-return air cylinders employ mechanical coil springs to provide the force that actuates the cylinder back to the fail-safe position in case of a compressed air supply failure. For air cylinders of large bore diameters, the mechanical coil springs must provide a return force of very large magnitude and, consequently, the size and weight of such mechanical coil springs becomes very large, which makes fail-safe or auto-return air cylinders employing mechanical coil springs very heavy, bulky and expensive. The present invention teaches how to construct a more economic fail-safe or auto-return air cylinder, which is lighter, more compact and cheaper than the conventional air cylinder by factors ranging from two to ten times compared with conventional auto-return air cylinders.
The primary object of the present invention is to provide an automatically returning air cylinder which employs the air-spring effect in place of the mechanical coil springs employed in conventional auto-return air cylinders.
Another object is to provide an automatically returning air cylinder employing the air-spring effect provided by compressed air or gas trapped in the air-spring chamber connected to a compressed air or gas supply through a check valve wherein the check valve provides the "self charging" and "self-recharging" capability of the air-spring chamber even when there is a minor leak from the air-spring chamber.
A further object is to provide an automatically returning air cylinder which is lighter in weight, more compact in bulk, less expensive in cost, and has a more powerful auto-return power compared with conventional auto-return air cylinders employing mechanical coil springs.
Still another object is to provide an automatically returning air cylinder which is as reliable as conventional auto-return air cylinders employing mechanical coil springs.
Still a further object is to provide an automatically returning air cylinder which automatically returns to the fail-safe position when the compressed air supply line supplying the compressed air to the air cylinder is intentionally vented or accidentally fails.
These and other objects of the present invention will become clear as the description thereof proceeds.